Exhaust gas recirculation is a method used in automotive vehicle internal combustion engines for exhaust emission control. One type of EGR valve is vacuum operated, being controlled by vacuum delivered from an EVR (electric vacuum regulator) valve. The latter valve is controlled by a signal from an engine ECU (electronic control unit) to provide the appropriate amount of vacuum to the EGR valve. The EVR valve comprises an inlet port communicated to a vacuum source, namely the engine manifold vacuum, and an outlet port communicated to a vacuum inlet port of the EGR valve. The EVR valve is energized by an electric signal, a pulse width modulated (PWM) signal for example, to regulate the vacuum applied to the EGR valve inlet port by causing the applied vacuum to correspond to the ECU signal; the EGR valve responds by providing a corresponding recirculation of engine exhaust gas.
A known EVR valve used in a gasoline engine application can provide a regulated vacuum output over a range extending to approximately 125 mm. Hg. The EVR valve that is disclosed in U.S. Pat. No. 4,850,384, the entirety of which is hereby incorporated herein by reference, is an example of such a valve.
When the range of vacuum output of a valve of that type is extended, for example in a diesel engine application where vacuum may extend to approximately 700 mm. Hg, the valve may experience certain undesired effects that could impair its performance and/or durability. It is believed that recalibrating the valve's magnetic air gap to a smaller dimension can extend the range, but may cause unacceptable drift as the valve is cycled. Reducing the diameter of the sealing surface of the valve disk can allow the air gap to be increased, but may cause increased wear on the valve disk and/or valve seat; it may also cause instability as the valve is cycled.